In the field of computer graphics (CG), when some manipulations such as move, rotation, and the like are applied to a geometric model defined on a three-dimensional (3D) space, that geometric model must be selected while being identified from other geometric models.
As a method of selecting an arbitrary one of a plurality of geometric models defined on an identical space, “Open Inventor” as a graphics library of SGI comprises a function of detecting a shape that intersects a line on the 3D space from those which form a virtual space (see “The Inventor Mentor Programming Object-Oriented 3D Graphics with Open Inventor, Release 2” Additon-Wesley, ISBN: 0-201-62495-8).
However, one geometric model is formed of a plurality of components. Therefore, if it has a geometrical relationship like that a given component (to be referred to as an occluded-component hereinafter) is occluded by another opaque component (group) (to be referred to as an occluding-component hereinafter), the occluded-component cannot be visually recognized in a CG image rendered by externally observing that geometric model. Therefore, in this case, it is impossible to interactively select occluded-components while observing the CG image.